1. Field of the Invention
The present invention is related to optical isolators for use in optical fiber communication and optical network technology, and more particularly to optical isolators which employ molded lenses.
2. Description of the Prior Art
In the field of optical fiber communications, problems with the performance of optical devices often arise. One such problem is caused by light reflecting off an end face or another part of an optical device. Such reflections can return to the light source, adversely affecting the light source and deteriorating the quality of communications. Another problem is caused by echoes of transmitted optical signals, which are caused by multiple reflections off the end face or another part of an optical device. The deterioration in performance of a light source due to the return of reflected light has been previously observed in connection with the stability of self-mode locking. Now, devices designed to eliminate reflected lights such as optical isolators, are used in optical fiber communication systems to prevent such deteriorated performance and eliminate reflected light.
FIG. 5 shown a conventional optical isolator as disclosed in U.S. Pat. No. 5,557,692. The optical isolator 80 comprises an input port 81, an output port 82 and an isolating means 83. The input port 81 comprises an input optical fiber 811 and a first Graded Index (GRIN) lens 812. The output port 82 comprises an output optical fiber 821 and a second GRIN lens 822. The isolating means 83 includes a first polarizer 831, a second polarizer 832 and a liquid crystal cell 833 disposed in the path of the rays from the first polarizer 831 to the second polarizer 832.
The conventional optical isolator 80 using GRIN lenses 812, 822 as collimating elements has some disadvantages. Firstly, the GRIN lenses are made using the ion-exchange method. However, this method requires a long time and further steps of polishing after initial formation, so it is difficult and expensive to manufacture. Secondly, some chemicals used in the ion-exchange method contaminate the environment and endanger the fabrication workers.
The present invention overcomes the above-described disadvantages of conventional optical isolators by offering an optical isolator having molded lenses which yield higher performance at a lower cost. A copending application Ser. No. 10/172,232 with the same assignee and the same inventors as the present invention discloses similar technology applied to other types of optical components.
Accordingly, an object of the present invention is to provide an improved optical isolator which employs molded lenses as collimating elements.
Another object of the present invention is to provide an optical isolator having high precision lenses which are relatively environmentally friendly to produce.
A further object of the present invention is to provide an optical isolator which is easily and cheaply manufactured.
To solve the problems of the prior art and to achieve the objects set forth above, an optical isolator of the present invention comprises an input port, an isolating means, an output port and a mounting tube. The input port comprises a ferrule having an optical fiber, a molded lens, a sleeve and a metal holder. The optical fiber has an exposed end and the ferrule defines a through hole for receiving and fixing the optical fiber therein. The ferrule has a rearward face and a forward face. The forward face of the ferrule is ground at an oblique angle and is flush with the exposed end of the optical fiber. The molded lens is cylindrical in shape and has an oblique surface coinciding with that of the ferrule and the exposed end of the optical fiber. A gap is defined between the molded lens and the ferrule. The output port is similar to the input port. The isolating means includes a first polarizer, a second polarizer and a Faraday rotator disposed in the paths of the rays from the first polarizer to the second polarizer. Furthermore, the optical axis of the second polarizer is oriented 45 degrees with respect to the optical axis of the first polarizer. The isolating means is located in the path of light beams from the input port to the output port.
Since the present invention employs molded lenses as the collimating elements, the cost and environmental problems associated with GRIN lenses are mitigated and efficiency is improved.
Other objects, advantages and novel features of the present invention will be apparent from the following detailed description of the preferred embodiment thereof with reference to the attached drawings, in which: